From: "Michael S. Tsirkin" <mst@redhat.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Hou Tao <houtao@huaweicloud.com>,
linux-fsdevel@vger.kernel.org, Vivek Goyal <vgoyal@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
linux-kernel@vger.kernel.org, virtualization@lists.linux.dev,
houtao1@huawei.com
Subject: Re: [PATCH] virtiofs: limit the length of ITER_KVEC dio by max_nopage_rw
Date: Sun, 25 Feb 2024 03:46:16 -0500 [thread overview]
Message-ID: <20240225034356-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CAJfpegsM2ViQb1A2HNMJLsgVDs1UScd7p04MOLSkSMRNeshm0A@mail.gmail.com>
On Fri, Feb 23, 2024 at 10:42:37AM +0100, Miklos Szeredi wrote:
> On Wed, 3 Jan 2024 at 11:58, Hou Tao <houtao@huaweicloud.com> wrote:
> >
> > From: Hou Tao <houtao1@huawei.com>
> >
> > When trying to insert a 10MB kernel module kept in a virtiofs with cache
> > disabled, the following warning was reported:
> >
> > ------------[ cut here ]------------
> > WARNING: CPU: 2 PID: 439 at mm/page_alloc.c:4544 ......
> > Modules linked in:
> > CPU: 2 PID: 439 Comm: insmod Not tainted 6.7.0-rc7+ #33
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), ......
> > RIP: 0010:__alloc_pages+0x2c4/0x360
> > ......
> > Call Trace:
> > <TASK>
> > ? __warn+0x8f/0x150
> > ? __alloc_pages+0x2c4/0x360
> > __kmalloc_large_node+0x86/0x160
> > __kmalloc+0xcd/0x140
> > virtio_fs_enqueue_req+0x240/0x6d0
> > virtio_fs_wake_pending_and_unlock+0x7f/0x190
> > queue_request_and_unlock+0x58/0x70
> > fuse_simple_request+0x18b/0x2e0
> > fuse_direct_io+0x58a/0x850
> > fuse_file_read_iter+0xdb/0x130
> > __kernel_read+0xf3/0x260
> > kernel_read+0x45/0x60
> > kernel_read_file+0x1ad/0x2b0
> > init_module_from_file+0x6a/0xe0
> > idempotent_init_module+0x179/0x230
> > __x64_sys_finit_module+0x5d/0xb0
> > do_syscall_64+0x36/0xb0
> > entry_SYSCALL_64_after_hwframe+0x6e/0x76
> > ......
> > </TASK>
> > ---[ end trace 0000000000000000 ]---
> >
> > The warning happened as follow. In copy_args_to_argbuf(), virtiofs uses
> > kmalloc-ed memory as bound buffer for fuse args, but
>
> So this seems to be the special case in fuse_get_user_pages() when the
> read/write requests get a piece of kernel memory.
>
> I don't really understand the comment in virtio_fs_enqueue_req(): /*
> Use a bounce buffer since stack args cannot be mapped */
>
> Stefan, can you explain? What's special about the arg being on the stack?
virtio core wants DMA'able addresses.
See Documentation/core-api/dma-api-howto.rst :
...
This rule also means that you may use neither kernel image addresses
(items in data/text/bss segments), nor module image addresses, nor
stack addresses for DMA.
> What if the arg is not on the stack (as is probably the case for big
> args like this)? Do we need the bounce buffer in that case?
>
> Thanks,
> Miklos
prev parent reply other threads:[~2024-02-25 8:46 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-03 10:59 [PATCH] virtiofs: limit the length of ITER_KVEC dio by max_nopage_rw Hou Tao
2024-01-09 12:01 ` Michael S. Tsirkin
2024-01-09 13:11 ` Bernd Schubert
2024-01-10 1:16 ` Hou Tao
2024-01-10 22:34 ` Bernd Schubert
2024-01-17 10:24 ` Hou Tao
2024-02-22 19:49 ` Michael S. Tsirkin
2024-02-23 0:58 ` Hou Tao
2024-02-23 9:42 ` Miklos Szeredi
2024-02-24 11:41 ` Hou Tao
2024-02-25 8:46 ` Michael S. Tsirkin [this message]
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